A double flywheel of the above kind is described in the specification of U.S. Pat. No. 4,903,544 and the corresponding French published patent application No. FR 2 626 336A. In those documents, the viscous damping means is arranged radially inward of the resilient means, being mechanically coupled between the two masses. The resilient means are housed in a first cavity.
The said viscous damping means includes a second sealed cavity which is filled with a second fluid, different from the fluid in the first cavity. The viscous damping means is mounted axially on one of the inertia masses. It is suitably dimensioned to suit the application intended for the double flywheel, in such a way as to give a predetermined degree of damping. The cavity is defined by two closure or cover members which are fixed to an external support element which acts as a spacer member. These cover members are joined to each other by means of screws which extend through the spacer member and which are fastened, at least in rotation and optionally with a clearance, to a damper plate.
Centring spigots are also provided for centring the spacer member and the cover plates.
With this arrangement, the radial size of the spacer member is such that it can accommodate these fastening screws and centring spigots, and sealing members are also necessary in this connection so as to ensure that the cavity is properly sealed. All this leads to an increase in the radial size of the viscous damping means, and calls for the use of a large number of components.